1. Field of the Invention
The control of weeds which grow in a wheat field after the wheat crop has been harvested has long been a problem to wheat farmers. The growth of the weeds has several disadvantages. The weeds, by their presence and growth, take needed moisture and nutrients from the soil, and prevention of this loss of moisture is particularly important in winter wheat production because of the relative scarcity of rainfall in those regions where winter wheat is grown. Further, the weeds are of no use as fodder for the farm animals. When the weeds mature, the seeds which are produced at maturity are scattered by the winds, birds, and animals, so that the infestation of weeds spreads far beyond the confines of the particular field.
2. Description of the Prior Art
The usual method of controlling the weeds in fallow wheatland has been to plow the field periodically, or otherwise cultivate it to kill the weeds. These operations kill the weeds so they do not mature and produce additional seeds, and so that the depletion of water from the soil by the weeds is prevented. The plowing and other cultivations do make the soil more friable and more receptive to rainfall, and the rainwater thereby does not run off and become lost.
However, the disadvantages of the usual method of controlling weeds in fallow wheatland are of such significance they are not to be overlooked. Control of the weeds by plowing usually requires about five plowings between the time of harvesting the wheat 1 year and the seeding of the new crop approximately 1 year later. Such plowings take time to accomplish. There is additional wear and tear on the machineary used by the wheat producer to accomplish the cultivations. The additional cultivations also loosen the soil and thus permit greater wind erosion of the soil. In addition, there is the increased consumption of fuel to power the machinery used in the cultivations. There would thus be significant overall savings to the producer together with benefit to the ecology if the number of man and machine operations on the soil could be reduced.
While the prior art refers to many thiadiazoles and derivatives thereof, none of the prior art is believed to be an enabling disclosure of the specific use disclosed herein. Some related compounds shown in the prior art, such as, for example, 1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-phenylthiourea and 1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-phenylurea [J. Pharm. Soc., Japan 74, 1044-1048 (1954); C.A. 49, 11630 (1955)] were not reported to have biological activity.
An article in Farmaco Ed. Sci. 22 (6), 393-401 (1967), discloses the use of 1-(5-alkyl-1,3,4-thiadiazol-2-yl)ureas as intermediates for the production of isomeric 1,3-bis-(5-alkyl-1,3,4-thiadiazol-2-yl) ureas, which latter compounds are alleged to exhibit hypoglycemic action. These compounds are only generally related to those used in the practice of the instant invention.
In U.S. Pat. No. 3,565,901 (Feb. 23, 1971), are taught salts of certain thiadiazol-2-ylureas alleged to be useful in agriculture applications as phytotoxicants. These salts are formed by thiadiazol-2-ylureas unsubstituted on the urea nitrogen closest to the thiadiazole ring. There is no mention of possible utility of the compounds in the cultivation of winter wheat and no test data regarding safety to winter wheat.
Belgian Pat. No. 765,930, teaches the use of 1,3-dimethyl-1-(5-tert.-butyl-1,3,4-thiadiazol-2-yl)urea, and 1-ethyl-1-(5-tert.-butyl-1,3,4-thiadiazol-2-yl)-3-methylurea, as pre- and postemergence herbicides on plant crops such as corn, cotton, peanuts, sorghum, and sugarcane. Data in this Belgian patent show that corn, cotton, sorghum, and wheat are largely destroyed by either pre- or postemergence application of from about 1 to about 5 pounds per acre of 1,3-dimethyl-3-(5-t-butyl-1,3,4-thiadiazol-2-yl)urea. This compound can also be named 1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea, and is one of the compounds disclosed in the instant application as being useful in the instant novel method. According to the Belgian patent, preemergence application of the same compound at rates of about 1 to about 10 pounds per acre to corn and cotton resulted in "no effect" to "destroyed." The Belgian patent also reports that the same treatments using 1-ethyl-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methylurea on corn, cotton, and sorghum, produced results ranging from "little effect" to "destroyed." The Belgian patent makes no suggestion that the compounds would be useful in the control of unwanted vegetation by preemergent application to a field wherein winter wheat is to be subsequently planted and grown.
In addition, Belgian Pat. No. 744,812, teached substituted 1,3,4-thiadiazoles, and alleges their utility as preemergence and/or postemergence herbicides, and as defoliants and dessicants of plants. No teaching of utility as selective herbicides appear to be present.
British Pat. No. 1,195,672, published June 17, 1970, teaches thiadiazoles alleged to possess utility as pre- and/or postemergence herbicides, together with herbicidal compositions containing the thiadiazoles as active ingredient, and a method of controlling plant growth. No suggestion that any of the compounds would be suitably selective for use as herbicides in the cultivation of winter wheat is present and winter wheat is not mentioned in the patent.
Yet another British Pat. No. 1,230,432, published May 5, 1971, is concerned with N-substituted 5-amino-1,3,4-thiadiazoles, the processes for their production, and their use as herbicides. A number of plants, including cotton, carrots, coffee, beans, beets, sugarcane, potatoes, bluegrass, barley, and wheat, as well as mustard, common chickweed, fescue, foxtail, and the like, are listed as susceptible to control by the N-substituted thiadiazoles. Thus, the control of desirable crop plants is made synonymous with the control of weed plants.
Still another British Pat. No. 1,254,468, published Nov. 24, 1971, is directed to 5-substituted 1,3,4-thiadiazolylureas, to processes for the production thereof, and to herbicidal compositions containing the named compounds. Utility for the control of weeds and wild grasses is alleged. No teaching is present of possible selectivity of herbicidal action of the compounds, nor utility in the cultivation of winter wheat.
British Pat. No. 1,266,172, published Mar. 8, 1972, is directed to substituted thiadiazole compounds and alleges their utility as herbicides, fungicides, acaricides, or insecticides. There appears to be no allegation in the British patent that the compounds listed therein would be useful as selective herbicides in the cultivation of winter wheat.
Kubo et al., J. Agr. Food Chem. 18 (1) 60-65 (1970), teach the results of the study of the preemergence and postemergence herbicidal activity of a number of 1-substituted-3-(5-substituted-1,3,4-thiadiazol-2-yl)ureas. The compound, 1-methyl-3-(5-t-butyl-1,3,4-thiadiazol-2-yl)urea, is reported as a strikingly phytotoxic compound. These authors report that this compound completely killed wheat when applied at the rate of 4.45 pounds per acre postemergence, but that it caused only slight damage to the wheat when applied at the same rate preemergence the day the seed was planted. However, preemergence tests in our laboratories using this compound at rates of 1, 2, and 4 pounds per acre killed the wheat.
Also in the prior art is British Pat. No. 1,297,147, published Nov. 22, 1972, which teaches 1,3,4-thiadiazolyl-(5)-ureas and their use as pre- or postemergence herbicides. The compounds are alleged to be particularly well suited for selective weed control in cereals, cotton, and carrots. In general, the application rate is taught as being from 0.9 to 110 lbs./acre, preferably from 1.9 to 44 lbs./acre. There is no teaching or disclosure suggesting use on fallow wheatland in the cultivation of winter wheat. In general, with few exceptions, the compounds tested killed wheat plants when applied either pre- or postemergent, according to the data disclosed in the patent.
A number of 2-ureido-5-sulphonamidothiazoles, alleged to possess utility as herbicides, are disclosed by West German Pat. No. 2,050,979, by Netherlands Pat. No. 7,015,249, and by Belgian Pat. No. 757,655. The abstracts of these publications, as appearing in Derwent, do not appear to suggest that the compounds were intended for use for the control of weeds in fallow wheatland.
The search continues for a satisfactory method of controlling the growth of unwanted vegetation in fallow winter wheatland, which method reduces the need to cultivate the land numerous times.